A Quick Note on Architecture & Features

With pages upon pages of architectural documents still to get through in only a few hours, for today’s launch news I’m not going to have the time to go in depth on new features or the architecture. So I want to very briefly hit the high points on what the major features are, and also provide some answers to what are likely to be some common questions.

Starting with the architecture itself, one of the biggest changes for RDNA is the width of a wavefront, the fundamental group of work. GCN in all of its iterations was 64 threads wide, meaning 64 threads were bundled together into a single wavefront for execution. RDNA drops this to a native 32 threads wide. At the same time, AMD has expanded the width of their SIMDs from 16 slots to 32 (aka SIMD32), meaning the size of a wavefront now matches the SIMD size. This is one of AMD’s key architectural efficiency changes, as it helps them keep their SIMD slots occupied more often. It also means that a wavefront can be passed through the SIMDs in a single cycle, instead of over 4 cycles on GCN parts.

In terms of compute, there are not any notable feature changes here as far as gaming is concerned. How things work under the hood has changed dramatically at points, but from the perspective of a programmer, there aren’t really any new math operations here that are going to turn things on their head. RDNA of course supports Rapid Packed Math (Fast FP16), so programmers who make use of FP16 will get to enjoy those performance benefits.

With a single exception, there also aren’t any new graphics features. Navi does not include any hardware ray tracing support, nor does it support variable rate pixel shading. AMD is aware of the demands for these, and hardware support for ray tracing is in their roadmap for RDNA 2 (the architecture formally known as “Next Gen”). But none of that is present here.

The one exception to all of this is the primitive shader. Vega’s most infamous feature is back, and better still it’s enabled this time. The primitive shader is compiler controlled, and thanks to some hardware changes to make it more useful, it now makes sense for AMD to turn it on for gaming. Vega’s primitive shader, though fully hardware functional, was difficult to get a real-world performance boost from, and as a result AMD never exposed it on Vega.

Unique in consumer parts for the new 5700 series cards is support for PCI Express 4.0. Designed to go hand-in-hand with AMD’s Ryzen 3000 series CPUs, which are introducing support for the feature as well, PCIe 4.0 doubles the amount of bus bandwidth available to the card, rising from ~16GB/sec to ~32GB/sec. The real world performance implications of this are limited at this time, especially for a card in the 5700 series’ performance segment. But there are situations where it will be useful, particularly on the content creation side of matters.

Finally, AMD has partially updated their display controller. I say “partially” because while it’s technically an update, they aren’t bringing much new to the table. Notably, HDMI 2.1 support isn’t present – nor is more limited support for HDMI 2.1 Variable Rate Refresh. Instead, AMD’s display controller is a lot like Vega’s: DisplayPort 1.4 and HDMI 2.0b, including support for AMD’s proprietary Freesync-over-HDMI standard. So AMD does have variable rate capabilities for TVs, but it isn’t the HDMI standard’s own implementation.

The one notable change here is support for DisplayPort 1.4 Display Stream Compression. DSC, as implied by the name, compresses the image going out to the monitor to reduce the amount of bandwidth needed. This is important going forward for 4K@144Hz displays, as DP1.4 itself doesn’t provide enough bandwidth for them (leading to other workarounds such as NVIDIA’s 4:2:2 chroma subsampling on G-Sync HDR monitors). This is a feature we’ve talked off and on about for a while, and it’s taken some time for the tech to really get standardized and brought to a point where it’s viable in a consumer product.

AMD Announces Radeon RX 5700 XT & RX 5700 Addendum: AMD Slide Decks
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  • Korguz - Tuesday, June 18, 2019 - link

    i said 22 ?? years old.. same as you.. my estimates ? you mean my exaggerations of how many FPS's quake would get on modern hardware ? just i wasnt sure about the age... maybe.. but that is just my thoughts too... will have to wait to see what street prices turn out to be when these are released.. they could very well be less then what amd has said. well.. thats what those i know said when i asked.. they dont play those games, so they see getting an rtx card as a waste of money.. but consider that they are comparing what they have now.. to getting an rtx card, and it could very well be a waste.. i am sure.. if they did play games that have rt in it.. they might be considering it.. again.. it really comes down to the games that have RT and if one plays them.. for myself, and the games i play.. i would be wasting my money.. but i have always wondered how one game i played would run on newer hardware/better hardware then i have currently, as it always brought my comp to its knees...my current 1060 strix with the 5939k @ 4.2 ghz, vs 1080ti or the 20series/radeon 7/5700xt, with a zen/zen 2 based cpu or a much newer intel cpu, a game called supreme commander... i read a review of it ages ago.. and if you didnt have at least a dual core, dont even bother.. with mine.. on the HUGE maps it has, and 1000 units per side ( up to 8 ) after about 20 mins.. im turning the game speed up to max, and lowering the eye candy down to at least the middle...
  • BenSkywalker - Tuesday, June 18, 2019 - link

    You had the question marks next to 22 years, I see contextually those were incredulous modifiers now, also your estimates, my frame rate goes from 1,460FPS to roughly 60FPS, it's much worse than 400 to 200.

    In no way am I asserting you are making a bad decision for you, not even close- what I'm saying is why would someone choose the 5700 over the 2060? Ignoring ray tracing all together they are close to identical in performance per dollar, so with one you can play around with it if you want, the other you can't.

    If you are saying neither are worth it, completely valid argument and I wouldn't argue it.
  • Korguz - Wednesday, June 19, 2019 - link

    heh.. my exaggeration was a little off for how fast quake would run ;-)

    well, until these cards are out ( 5700 series ) its hard to say if they will be priced that close together, currently the 2060's are priced between 500 and up to 570, even if the entry level 5700 is less then 500 then it could be a better buy.. but wont know for sure for a few more weeks...

    right now.. i guess in a way i am, cause they dont provide a big enough performance increase over what i or those i know.. currently have... my self.. i would need to go to at least a 2070/5700xt.
  • BenSkywalker - Wednesday, June 19, 2019 - link

    Newegg.ca has the Asus phoenix 2060 for $449, a large selection for under $480. At a direct currency exchange the 5700 will be $508 in Canada.
  • Korguz - Wednesday, June 19, 2019 - link

    ahh yes.. the newegg angle.. are you also factoring potenial shipping costs ?? currency exchange.... moot point as that changes daily... and can vary.
    i will wait to see what prices are when released... then compare...
  • BenSkywalker - Wednesday, June 19, 2019 - link

    That's NewEgg Canada, not the U.S., is shipping different for some reason? There is no currency conversion on the newegg.ca site if you're in Canada.

    Obviously waiting for reviews will give us a fuller picture, my issue is what they claimed just doesn't seem to have any compelling reason to buy it over the competition.
  • Korguz - Thursday, June 20, 2019 - link

    BenSkywalker i was referring to newegg.ca in regards to shipping, but seems they have free shipping on that gpu ATM.. either way.. still something to consider if newegg as anything cheaper then going to a local store as with shipping, could negate the lower initial price. as for currency convert.. that was in regards to the 5700.. as there is no current cdn prices... yet...
  • powerwiz - Tuesday, June 18, 2019 - link

  • Slashchat - Tuesday, June 18, 2019 - link

    and where are the 5800 xt and 5900 dual navi xt?
  • m16 - Sunday, June 23, 2019 - link

    I'd love to get one of these. Nvidia has basically had the market for too long and they now force you to have an account and telemetry enabled to have gaming driver updates and optimizations. They've really not gotten any good karma with me or anyone caring about privacy.

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